Mu-opioid receptor (MOR) expression in the human spiral ganglia

Abstract

Opioid peptides and their receptors have been localized to the inner ear of the rat and guinea pig mammalian models. The expression of mu opioid receptor (MOR) in the human and mouse cochlea is not yet known. We present MOR protein localization by immunohistochemistry and mRNA expression by in situ hybridization in the human and mouse spiral ganglia (SG) and organ of Corti. In the human most of the (SG) neurons were immunoreactive; a subset was non-immunoreactive. In situ hybridization revealed a similar labeling pattern across the neurons of the SG. A similar distribution MOR pattern was demonstrated in the mouse SG. In the mouse organ of Corti MOR was expressed in inner and outer hair cells. Fibers underneath the inner hair cells were also MOR immunoreactive. These results are consistent with a role of MOR in neuro-modulation of the auditory periphery. The present results show that the expression of MORs is well-conserved across multiple mammalian species, indicative of an important role in auditory processing.

Immunohistochemical techniques for the human inner ear

“…Earlier studies utilized cytologic descriptions and graphic reconstructions of the cochlea (Guild 1921). Temporal bone science has advanced such that we are now entering a phase of methodological integration, whereby the same temporal bone can be used for light microscopy, transmission electron microscopy (TEM), immunohistochemistry (IHC), non-radioactive in situ hybridization, DNA and proteomics analysis (Aarnisalo et al 2010; Kong et al 1998; Merchant et al 2008; Ishiyama et al 2009, 2010; Lopez et al 2005a, b, 2007; Markaryan et al 2008a, b, c, 2009a, b, c, 2010a, b; Nguyen et al 2014; Richard et al 2015; Schrott-Fischer et al 1994, 2002a, b, 2007; Wackym et al 1990). The study of the human inner ear has lagged behind other areas of pathology, in large part due to the inaccessibility of the membranous labyrinth.…”

“…An additional advantage is the ability to apply unbiased stereology in immunostained endorgans (Lopez et al 2005a). Additionally, it is also possible to use vestibular endorgans microdissected from human temporal bones to extract mRNA to evaluate the expression of muscarinic acetylcholine receptors (Wackym et al 1996) or mu-opioid receptor mRNA expression by non-radioactive in situ hybridization (Nguyen et al 2014). …”

“…The specimens are serially sectioned at 20 μm, and every tenth section is stained with hematoxylin and eosin. The celloidin-embedding method yields superb morphological and histopathological preservation of the human inner ear that can be used for IHC (Ganbo et al 1997, 1999; Cunningham et al 2001; Keithley et al 1994, 2000; Markaryan et al 2011; Ying and Balaban 2009; Ahmed et al 2013; Balaker et al 2013; Nguyen et al 2014; Vorasubin et al 2016). It is important to have in consideration the length of fixation specially for IHC.…”

“…Methanol–sodium hydroxide method completely removed celloidin and produced good immunostaining with six antibodies: prostaglandin D synthase, Na + K + -ATPase, aquaporin 1, connective tissue growth factor, tubulin and 200kd neurofilaments. We used sodium ethoxide to remove celloidin from the sections and obtain very good immunoreactive signal with almost no background (Calzada et al 2012a, b; Ahmed et al 2013; Balaker et al 2013; Nguyen et al 2014; Vorasubin et al 2016). …”

Noise-induced hearing loss: Neuropathic pain via Ntrk1 signaling

“…Intense sounds are not only perceived as painfully loud (Ades et al, 1959), but can also induce pain sensations in around the external ear (otalgia; Dominguez et al, 2006; Hebert et al, 2013; Henry et al, 2014; Kaltenbach et al, 2000; Knipper et al, 2013; McFerran and Baguley, 2007; Norena, 2011; Pienkowski et al, 2014; Tyler et al, 2014a; Van Campen et al, 1999; Westcott et al, 2013). Pain transmitting neuropeptides and receptors are present in the CN and auditory nerve (Aguilar et al, 2004; Bauer et al, 2007b; Jongkamonwiwat et al, 2003; Nguyen et al, 2014; Phansuwan-Pujito et al, 2003; Tongjaroenbuangam et al, 2006), raising the possibility that loud sounds may trigger the perception of pain through these signaling pathways.…”